This invention relates to the removal of water from a mixture of water and certain solid residues of carbonaceous material, such as coal char, and is particularly concerned with an efficient and relatively simple process for agglomerating the particles of such solid residues, particularly coal char, in a char-water slurry, and further processing the resulting mixture to remove the agglomerated carbonaceous solids or char, to obtain a carbonaceous solids or char product of substantially reduced water content.
The agglomeration of bituminous coal by use of hydrocarbons has been demonstrated, as described in Perrott, G. St. J., and Kinney, S. P., "Laboratory Studies of the Trent Process," USBM No. 2263, July, 1921; and Fraser, T., "Convertol Process of Coal-Slurry Treatment," USBM No. I.C. 7660, April, 1953. Dewatering of a coal-water slurry by the use of surfactants has also been reported in Silverblatt, C. E. and Dahlstrom, D. A., "Moisture Content of a Fine-Coal Filter Cake," Industrial and Engineering Chemistry, June, 1954; Venkatesan, S., "Research Imperative to Improve Thermal Drying," Coal Mining and Processing, September, 1975; and Baker, A. F., "Hot Surfactant Solution as a Dewatering Aid During Filtration," NCA/BCR Coal Conference and Expo III, Louisville, Ky., October, 1976. However, these applications have been limited to a neutral water-slurry system.
U.S. Pat. No. 3,349,029 discloses a process for removing carbon particles from quench water by first treating the carbon particles with a surfactant capable of rendering the particles hydrophobic, contacting the particles with a liquid hydrocarbon to transform the carbon particles to larger units such as balls, and separating such larger carbon units from the aqueous medium by suitable means such as filtration. Processing temperatures disclosed are at 160.degree. F. to 180.degree. F. The quench water is apparently substantially neutral. U.S. Pat. No. 3,717,574 discloses addition of an acid such as sulfuric to a normally alkaline colloidal coal slurry and thereafter flocculating the slurry by addition of polyacrylamides and similar agents. The reaction pH is just on the acid side, about 6.5.
U.S. Pat. Nos. 3,268,071; 3,661,254; 4,003,737 and Sirianni et al., Recent Experience with the Spherical Agglomeration Process, Can. J. Chem. Engr., Vol, 47, pp. 166-170, April, 1969, all deal with the Canadian spherical agglomeration process, employing hydrocarbons and which is applicable to a wide variety of material separations including coal and graphite. The 3,661,254 patent discloses agglomeration at both high and low pH using a combination of materials such as sodium oleate and crude oil.
U.S. Pat. Nos. 2,903,423; 3,210,170 and 3,694,355 relate to an agglomeration process applicable to carbon-water and coal-water slurries, employing hydrocarbons.
U.S. Pat. Nos. 3,462,262 and 3,917,569 are also illustrative of technique for separating carbon from a water-carbon slurry, e.g. by hydrocarbon addition.
However, certain particulate residues of carbonaceous substances, such as coal char, cannot be agglomerated effectively from an aqueous neutral slurry thereof by addition of hydrocarbon or surfactant, separately, or in combination.
It is an object of the present invention to remove water from aqueous mixtures containing particulate carbonaceous solids. A further object is the provision of effective procedure to facilitate the removal of water in mixtures of water and certain solid residue particles of carbonaceous material, particularly coal char, by agglomeration of such particles and the displacement of the water from the agglomerate through the use of an immiscible liquid. Yet another object is to provide procedure of the above type whereby following agglomeration of the residue solids, e.g. coal char, particles, and displacement of water from the agglomerated particles, the water content of such particles, after screening, can be substantially reduced by techniques including filtering and/or centrifuging.